Analytical solution for dynamic behavior of multiwall carbon nanotubes subjected to mechanical shock loading

Dynamic behavior and frequency analysis of multiwall carbon nanotubes (MWCNTs) with finite length are investigated using an analytical method. By applying multiple elastic shells and a linearized model of van der Waals forces, a comprehensive continuum dynamic model of MWCNTs is developed. Also, by utilizing Laplace transform, time histories of MWCNTs subjected to shock lading are obtained. Then by using the fast Fourier transform (FFT), the time responses are transferred to the frequency domain and natural frequencies are found. The accuracy of results is verified by comparing the results of sudden loading with those obtained by numerical methods. Furthermore, an abrupt unloading after ramp loading is simulated, and the dependency of diameter and length on the axial and radial natural frequencies of MWCNTs is examined. Also, by characterizing the longitudinal displacement, the wave propagation velocities are obtained and an explicit expression is found for the axial natural frequencies of MWCNTs subjected to shock loading.     

Extended Kalman Filter frequency tracker for nonstationary harmonic signals

In this paper, we propose a frequency tracking algorithm based on an Extended Kalman Filter (EKF). We introduce a generalized state space model to estimate and track frequency of a harmonic signal embedded in broad-band noise. Such nonstationary noisy harmonic signals are characterized by time-varying frequencies and amplitudes. Developing a modified state-space model, we improve performance of EKF frequency tracker for these signals. The proposed method is also used in an adaptive algorithm to estimate noise variance which is assumed to be unknown. Simulation results reveal superiority of the proposed method compared with typical EKF, short time Fourier transform, and interpolated discrete Fourier transform.     

Nanoscale surface deformation inspection using FFT and phase-shifting combined interferometry

In this paper, a flexible optical interferometer incorporated with both fast Fourier transform (FFT) and phase-shifting method is developed for three-dimensional (3D) testing of micro-components. Using light interference, microscopic optics, piezoelectric transducer (PZT) nanoscanning and a CCD camera, the proposed system can detect deformation and surface contour in the order of nanometers. An application of the proposed technique is demonstrated using two micro-components: a micro-beam in an accelerometer and a micromirror. The resulting interference fringes that are related to the deformation and surface contour are analyzed using FFT method or three-step phase-shifting method depending on the test surface features. Experimental results show the feasibility of the proposed method for 3D deformation and surface contour measurement of micro-components.     

Frequency Loss and Recovery in Rolling Bearing Fault Detection

Rolling element bearings are key components of mechanical equipment. The bearing fault characteristics are a ected by the interaction in the vibration signals. The low harmonics of the bearing characteristic frequencies cannot be usually observed in the Fourier spectrum. The frequency loss in the bearing vibration signal is presented through two independent experiments in this paper. The existence of frequency loss phenomenon in the low frequencies, side band frequencies and resonant frequencies and revealed. It is demonstrated that the lost frequencies are actually suppressed by the internal action in the bearing fault signal rather than the external interference. The amplitude and distribution of the spectrum are changed due to the interaction of the bearing fault signal. The interaction mechanism of bearing fault signal is revealed through theoretical and practical analysis. Based on mathematical morphology, a new method is provided to recover the lost frequencies. The multi-resonant response signal of the defective bearing are decomposed into low frequency and high frequency response, and the lost frequencies are recovered by the combination morphological filter(CMF). The e ectiveness of the proposed method is validated on simulated and experimental data.     

基于小波有限元法的悬臂梁裂纹识别的试验研究

利用小波有限元法求解了裂纹悬臂梁的前三阶固有频率,并将其拟合成以裂纹位置和深度作为变量的固有频率解曲面;将实测的裂纹梁前三阶固有频率作为裂纹识别反问题的输入,绘制出各阶固有频率等高线,三条等高线的交点预测出裂纹存在的位置和深度。试验结果验证了算法的有效性,这为其实际应用提供了有力的试验依据。     

基于傅里叶描述子的平面物体表征与抓取规划

针对传统抓取规划方法难以计算复杂轮廓物体、计算量大耗时长的弊端,以及基于深度学习的抓取规划方法物理模型简单、训练集制作耗时长的缺陷,提出了一种基于傅里叶描述子的平面物体表征及抓取规划方法。对物体进行图像采集和轮廓提取,将以散点形式表示的轮廓转化为傅里叶描述子,提取高阶项从而还原物体轮廓,构造了轮廓的参数方程。根据轮廓参数方程和接触点位置,使用不同接触模型构造抓取映射矩阵,采用凸包推进算法计算不同抓取位姿在力 力矩空间上的抓取性能指标。基于抓取性能指标,采用一种改进的粒子群方法进行抓取点规划,在二指夹持器和四指夹持器模型上进行了仿真验证。     

基于DLP数字微镜的结构光三维扫描系统

为了提高现代化生产中的效率和满足三维扫描的需求,设计了一种能够准确提取物件表面三维轮廓信息的扫描系统。系统采用结构光三维成像方法,先通过普通白光将光栅投影到被测物体表面,利用工业相机采集变形光栅图,再根据变形光栅图像中的灰度值变化,用傅里叶变换轮廓法解调出三维坐标信息。实验结果表明,使用傅里叶变换轮廓法重构可获得效果理想的三维点云,其为三维轮廓扫描提供了实验方法,同时也为提高点云精度提供参考。     

基于边等距偏移的环切加工刀具路径生成方法

针对由直线和圆弧组成的封闭轮廓生成环切加工刀具路径的问题,提出了一种基于边等距偏移的环切加工刀具路径生成方法。该方法分别从封闭轮廓的凸点和干涉凹点出发,结合边干涉检测程序和圆弧边分段处理方法对包含直线和圆弧的轮廓分别进行局部和全局无效区域检测,删除轮廓的无效区域后进行等距偏移,生成无干涉环切加工路径。利用自主开发的CAD/CAM软件实现了该方法,仿真实验结果表明,该方法能够准确、有效地生成无干涉区域的刀具加工路径,同时适用于带有孤岛的封闭轮廓偏移。     

利用传递矩阵法对阶梯悬臂梁的裂纹参数识别

基于Bernoulli-Euler梁振动理论,以等效弹簧模拟裂纹引起的局部软化效应,利用传递矩阵法推导阶梯悬臂梁振动频率的特征方程,对于含多个裂纹以及复杂边界条件的阶梯梁,仅需求解4×4的行列式即可获得相应的频率特征方程。直接利用该特征方程,提出两种有效估计裂纹参数的方法———等值线法和目标函数最小化法,并应用两段阶梯悬臂梁的数值算例说明方法的有效性。算例结果表明,只需结构前三阶频率即可识别裂纹位置和深度。应用“零设置”可减小计算频率与理论频率不相等对识别结果的影响。等值线法可以直观给出裂纹位置和裂纹深度参数,目标函数最小化法可给出最优的裂纹参数结果,并且该方法可推广应用到含多个裂纹复杂梁(如非完全固支、弹性支撑等)结构的裂纹参数识别中。     

基于网格拓扑关系追踪的等值线生成方法

等值线图广泛应用于工程分析和科学计算领域。提出了一套基于三角形网格拓扑关系追踪的等值线生成算法。先计算出网格顶点的场量值，然后根据每条网格边所涉及的顶点判断并确立网格边上的等值点，最后根据三角形网格的拓扑关系追踪每条等值线。与其他算法相比，该算法减少了内存消耗和计算量，大大提高了等值线的生成速度和处理效率。最后以实例验证了该算法的有效性。     

两端支座松动转子系统的频率特性分析

针对转子-轴承系统中两端支座发生的松动故障,建立了带有非线性油膜力的数学模型。采用数值仿真的方法对发生故障的转子系统进行模拟,得到了系统的频率特性。模拟结果表明：当支座发生松动振动时,若振动位移小于最大间隙值,则它的频谱除了1倍频分量外还有丰富的且相对幅值较大的低频成分;若振动位移大于最大间隙值,则它的频谱会出现非常突出的较高倍频的分量, 而1倍频却消失了。得出的结论有助于对该类故障的诊断分析。     

A comb-sampling method for enhanced mass analysis in linear electrostatic ion traps

In this paper an algorithm for extracting spectral information from signals containing a series of narrow periodic impulses is presented. Such signals can typically be acquired by pickup detectors from the image-charge of ion bunches oscillating in a linear electrostatic ion trap, where frequency analysis provides a scheme for high-resolution mass spectrometry. To provide an improved technique for such frequency analysis, we introduce the CHIMERA algorithm (Comb-sampling for High-resolution IMpulse-train frequency ExtRAaction). This algorithm utilizes a comb function to generate frequency coefficients, rather than using sinusoids via a Fourier transform, since the comb provides a superior match to the data. This new technique is developed theoretically, applied to synthetic data, and then used to perform high resolution mass spectrometry on real data from an ion trap. If the ions are generated at a localized point in time and space, and the data is simultaneously acquired with multiple pickup rings, the method is shown to be a significant improvement on Fourier analysis. The mass spectra generated typically have an order of magnitude higher resolution compared with that obtained from fundamental Fourier frequencies, and are absent of large contributions from harmonic frequency components.     

机床整机动刚度薄弱环节辨识与优化方法研究

提出一种机床整机动态分析指导薄弱部件改进的优化思路,即通过对机床整机的动刚度进行分析,辨识出不同激振频率下整机中的薄弱环节,明确优化目标,提高优化效率。利用ANSYS Workbench软件对一种卧式加工中心进行谐响应分析和模态分析,辨识出立柱是整机x向和z向动刚度的最薄弱环节。以立柱结构为优化对象,运用灵敏度分析法计算出立柱质量和固有频率对各个壁板的灵敏度。以立柱固有频率为优化目标,立柱质量为约束条件,建立优化方程。利用Matlab软件求解该方程,得到立柱的优化结果。通过谐响应分析得到优化后机床整机的动刚度,结果表明,优化后立柱在质量不增加的情况下,整机在x向和z向的最大共振峰值降低约6.5%,相应的共振频率提高约10%。     

视觉驱动的语音合成系统中唇形轮廓的正交变换描述

为了能够自动而且快速地获取唇读系统中所必需的唇形轮廓特征,提出了将正交压缩变换的方法用于唇形轮廓的特征提取,并对得到的唇形轮廓曲线进行了分析研究。通过离散傅里叶变换(DFT)和离散余弦变换(DCT)分别得到描述唇形轮廓特征的傅里叶描述子和离散余弦变换描述子,然后将两类描述子作为唇形轮廓的特征向量,采用隐马尔可夫模型(HMM)进行学习和识别。基于独立汉字发音的实验表明:在达到40％的识别率时,刻画唇形轮廓特征所需的离散余弦变换描述子数目为15个,傅里叶描述子数目为20个。在相同的识别效果时,刻画唇形轮廓特征所需的离散余弦变换描述子数目少于傅里叶描述子,可减少数据运算量和运算所需时间。     

Vibration analysis of rectangular plates with edge V-notches

A method is presented for accurately determining the natural frequencies of plates having V-notches along their edges. It is based on the Ritz method and utilizes two sets of admissible functions simultaneously, which are (1) algebraic polynomials from a mathematically complete set of functions, and (2) corner functions duplicating the boundary conditions along the edges of the notch, and describing the stress singularities at its sharp vertex exactly. The method is demonstrated for free, square plates with a single V-notch. The effects of corner functions on the convergence of solutions are shown through comprehensive convergence studies. The corner functions accelerate convergence of results significantly. Accurate numerical results for free vibration frequencies and nodal patterns are tabulated for V-notched square plates having notch angle α=5° or 30° at different locations and with various notch depths. These are the first known frequency and nodal pattern results available in the published literature for rectangular plates with V-notches.     

基于自适应技术的铁路FSK信号检测

铁路通信系统中主要采用的信号制式为国产移频信号和UM71信号,其表现形式均为二进制频移键控信号。采用自适应技术,分别以信号中的两个载频作为自适应滤波器的期望信号,提取其中某一频率分量,进而得到调制信号的包络求解调制频率,并结合后续频域算法得到两个载频的精确值。以铁路实测数据作为分析对象验证算法,实现了对信号的高精度检测。     

小波变换轮廓术测量精度影响因素的研究

对影响小波变换轮廓术测量精度的部分因素进行了研究。首先,为了考察光栅频率和入射角对测量精度的影响,获得合适的光栅频率和入射角,对不同光栅频率和入射角下的半圆形轮廓进行了研究;然后,为了研究不同的小波母函数对相位提取精度的影响,使用不同的小波母函数对半圆形轮廓进行小波变换,分析不同的小波母函数对半圆形轮廓测量精度的影响;最后,通过对钢板进行重建验证,研究发现了决定小波变换轮廓术测量精度的一些因素,重建钢板的厚度误差不超过 0.05 mm 。     

On the natural frequencies of helical compression springs

The linearized disturbance equations governing the resonant frequencies of a helical spring subjected to a static axial compressive load are solved numerically using the transfer matrix method for clamped ends and circular cross-section to produce frequency design charts. The effect of varying the number of turns of the spring is investigated, and in the limit of large numbers of turns, our results validate earlier work on the vibration of helical compression springs in which the helix was modeled as an elastic beam with rigidities corresponding to those of unclosed circular rings.     

A Fast and Efficient Approach for Image Compression Using Curvelet Transform

In this paper a novel image compression technique using features of wavelet and curvelet transforms is proposed to improve efficiency and compression performance. Indeed, the curvelet transform is one of the recently developed multiscale transforms which is especially designed to represent efficiently curves and edges in an image. In the proposed method, the compression algorithm involves the Haar wavelet transform to decompose the image into four frequency sub-bands. The lowest frequency sub-band coefficients are processed using Set Partitioning In Hierarchical Trees (SPIHT) encoding. Meanwhile, Fast Discrete Curvelet Transform (FDCT) is applied to the remaining frequency sub-bands. The FDCT output coefficients are then quantized according to the sub-band they belong to. The lowest frequency FDCT output coefficients are quantized using Differential Pulse Code Modulation, the medium frequency coefficients are processed using SPIHT, whereas the high frequency coefficients are removed. Experimental results demonstrate that our method provides high performance for edge detection compared to existing techniques particularly for images with abrupt changes. In addition, this new image coding and decoding approach is powerful in terms of computation time. Moreover, the proposed method reveals significant improvement in compression ratio and decoded peak-signal-to-noise-ratio.     

基于电机电流经验模态分解的行星轮故障诊断

在故障诊断领域,电机电流信号分析法(MCSA)已经逐渐应用于齿轮故障诊断中,但该方法在诊断行星轮缺齿故障时由于电流基频干扰较大,导致故障特征不明显,难以实现故障诊断。因此提出一种基于电流信号经验模态分解(EMD)的故障诊断方法。通过对电机电流信号进行EMD分解,选取合适的IMF分量经傅立叶变换求其频谱图,根据频谱图中是否存在与故障特征频率相关的频率,实现了对行星轮缺齿故障的有效诊断。并通过实验分析,验证了该方法的有效性。